This invention relates generally to pressure compensated or load responsive valves which utilize either positive or negative load controllers. Such valves control positive or negative loads, the displacement of the valve spool from its neutral position being proportional to the flow delivered to the load.
In more particular aspects this invention relates to the synchronization and transmittal of pressure control signals from valve chambers to valve controllers, while those chambers are being interconnected by the valve spool.
It is very desirable to isolate the load chamber of the pressure compensated or load responsive valve from the valve controllers with the valve spool in a neutral position while no work is being performed by hydraulic system. This permits unloading of the pump and avoids leakage losses in the controllers thus increasing system efficiency.
It is also very desirable to transmit to the valve controllers a load pressure signal before flow through the valve begins, so that those controllers can assume their controlling position in anticipation of flow demand.
This function is accomplished by providing a pressure signal passage connecting the valve bore in the region of the partition dividing valve chambers to the valve controller. In the neutral position of the valve spool this pressure signal passage is blocked by a land of valve spool, the initial displacement of valve spool from the neutral position first interconnecting the load chamber with the pressure signal passage and the valve controller and upon further displacement of valve spool, interconnecting the load chamber with either the inlet chamber or the outlet chamber. This method of transmittal of control signals is shown in my U.S. Pat. No. 3,444,689 dated May 20, 1969, my U.S. Pat. No. 3,470,694 dated Oct. 7, 1969, my U.S. Pat. No. 3,744,517 dated July 10, 1973, my U.S. Pat. No. 3,858,393 dated Jan. 7, 1975, my U.S. Pat. No. 3,882,896 dated May 13, 1975, my U.S. Pat. No. 3,998,134 dated Dec. 21, 1976 and U.S. Pat. No. 3,488,953 dated Jan. 13, 1970 issued to Haussler.
However, while this method is very effective in transmitting the load control signal prior to cross connecting valve chambers, it suffers from certain basic disadvantages. Since the drilled pressure signal passage is located in the partition between the valve chambers, in order not to excessively increase the dead band of the valve which is very harmful since it reduces the length of the effective control stroke, the diameter of pressure signal passage must be kept small, resulting in serious attenuation of control signal and high cost of manufacture. Even with a small pressure signal passage the resulting dead band of the valve becomes excessive for some applications.
This method also prevents close synchronization of valve spool timing in control of positive and negative loads.